Arachidonic acid in adipose tissue is associated with nonfatal acute myocardial infarction in the central valley of Costa Rica

Arachidonic acid (AA), a precursor of prothrombotic eicosanoids, is potentially atherogenic, but epidemiologic data are scarce. We evaluated the hypothesis that increased AA in adipose tissue is associated with increased risk of nonfatal acute myocardial infarction (MI), and if so, whether this association is related to dietary or adipose tissue linoleic acid. We studied the association between AA and MI in 466 cases of a first nonfatal acute MI, matched on age, gender, and residence to 466 population controls. Fatty acids (FA) were assessed by GC in adipose tissue samples collected from all subjects. Odds ratios (OR) and 95% CI were calculated from multivariate conditional logistic regression models. Subjects in the highest quintile of adipose tissue AA (0.64% of total FA) had a higher risk of nonfatal acute MI than those in the lowest quintile (0.29% of total FA), after adjusting for potential confounders including (n-3) and trans FAs (OR = 1.94, 95% CI: 1.07, 3.53, P for trend = 0.026). Adipose tissue AA was not correlated with dietary AA (r = 0.07), linoleic acid (r = 0.04), or other dietary (n-6) FAs, or with adipose tissue linoleic acid (r = -0.07). These data suggest that the association between MI and adipose tissue AA is not related to dietary intake of (n-6) FAs including linoleic acid. Better understanding of the metabolic factors that increase AA in adipose tissue is urgently needed.

Changes in Milk Fat in Response to Dietary Supplementation with Calcium Salts of Trans-18:1 or Conjugated Linoleic Fatty Acids in Lactating Dairy Cows

Milk fat was investigated in lactating dairy cows fed diets supplemented with Ca salts of trans fatty acids (Ca-tFA) or Ca salts of conjugated linoleic acids (Ca-CLA). Forty-five Holstein cows (115 days in milk) were fed a control diet (51% forage; dry matter basis) supplemented with 400 g of EnerG II (Ca salts of palm oil fatty acids) for 2 wk; subsequently, 5 groups of 9 cows each were assigned for 4 wk to the control diet or diets containing 100 g of Ca-CLA or 100, 200, or 400 g of Ca-tFA in a randomized block design. Treatments had no effect on dry matter intake, milk production, protein, lactose, or somatic cell count. Milk fat percentage was reduced from 3.39% in controls to 3.30, 3.04, and 2.98%, respectively, by the Ca-tFA diets and to 2.54% by the Ca-CLA diet. Milk fat yield (1.24 kg/d in controls) was decreased by 60, 130, and 190 g/d with increasing dose of Ca-tFA and by 290 g/d with the Ca-CLA supplement. Consistent with increased endogenous synthesis of cis-9-containing CLA from precursors provided by the Ca-tFA diets, total CLA were similar in milk of cows fed Ca-CLA or Ca-tFA. Compared with controls, the Ca-CLA diet increased trans-10, cis-12-18:2 yield in milk, without altering levels of trans-18:1 isomers. In contrast, yields of most trans-18:1 isomers were elevated in milk of cows fed Ca-tFA diets, whereas yields of trans-10, cis-12-18:2 remained similar to control values. We conclude that milk fat depression can occur without an increase in trans-10, cis-12-18:2 in milk and that other components, perhaps the trans-10-18:1 isomer, may be involved.

Prolonged feeding of mice with conjugated linoleic acid increases hepatic fatty acid synthesis relative to oxidation

Feeding mice conjugated linoleic acid (9 cis,11 trans/9 trans,11 cis-and 10 trans,12 cis-CLA in equal amounts) resulted in triacylglycerol accumulation in the liver. The objective of this study was to examine whether this steatosis is associated with changes in hepatic fatty acid synthesis and oxidation. Therefore, we measured the activities of key enzymes of fatty acid synthesis, i.e., acetyl-CoA carboxylase and fatty acid synthase and of fatty acid oxidation, i.e., 3-hydroxy-acyl-CoA dehydrogenase and citrate synthase in livers of mice fed a diet with 0.5% (w/w) CLA. CLA (a 1:1 mixture of the 10 trans, 12 cis and 9 cis, 11 trans isomers of octadecadenoic acid) was administered for 3 and 12 weeks with high-oleic sunflower oil fed as control. The proportion of body fat was significantly lower on the CLA than on the control diet and this effect was already significant after 3 weeks. The specific activites of 3-hydroxy-acyl-CoA dehydrogenase and citrate synthase were unaffected by CLA both after 3 and 12 weeks. The specific activity of fatty acid synthase was nonsignificantly raised (by 12%) after 3 weeks on the CLA diet but had increased significantly (by 34%) after 12 weeks of feeding. The specific activity of acetyl-CoA carboxylase had also increased both after 3 weeks (by 53%) and 12 weeks (by 23%) on the CLA diet, but this effect did not reach statistical significance. Due to CLA-induced hepatomegaly, the overall capacity for both fatty acid oxidation and synthesis-as evidenced by the total hepatic activities of 3-hydroxy-acyl-CoA dehydrogenase, citrate synthase, acetyl-CoA carboxylase, and fatty acid synthase-was significantly greater in the CLA-fed group after 12 weeks, although the overall capacity for fatty acid synthesis had increased more than that for fatty acid oxidation. Thus, this study indicates that prolonged, but not short-term, feeding mice with CLA increased hepatic fatty acid synthesis relative to oxidation, despite the decrease in body fat and the increase in liver weight seen earlier. It is concluded that the observed CLA-induced changes in hepatic fatty acid synthesis and oxidation are the result, rather than the cause, of the lowering of body fat.

The effect of dietary supplementation with linoleic acid to late gestation ewes on the fatty acid composition of maternal and fetal plasma and tissues and the synthetic capacity of the placenta for 2-series prostaglandins

Linoleic acid (18:2n-6) is metabolised to arachidonic acid (20:4n-6), the precursor for 2-series prostaglandins (PGs). Increased consumption of 18:2n-6 during pregnancy may thus modify PG synthesis during labour. We have investigated whether increased 18:2n-6 composition during gestation altered the fatty acid consumption and PG synthesis of maternal and fetal tissues in the sheep. Ewes were fed a control diet or a diet providing 40% more 18:2n-6 from 96 days gestation. Half of each group received dexamethasone on day 136 to up-regulate the PG synthetic pathways promoting parturition. Maternal and fetal tissues were collected at 138 days. The 18:2n-6 diet significantly increased the 20:4n-6 content of maternal plasma, fetal plasma and allantochorion (51-81%) phosphatidylcholine, and fetal liver (40%) and maternal caruncular endometrium (57%) phosphatidylethanolamine. Increased 18:2n-6 intake increased production of PGF(2alpha) and PGE(2) in all placental tissues (maternal caruncular and intercaruncular endometrium and fetal allantochorion) by 23-98%, whereas dexamethasone increased it by 32-142%. This suggests that consumption of an 18:2n-6-enriched diet in late pregnancy enhanced placental PG production by increasing the supply of 20:4n-6. Variations in the extent to which the diet altered the polyunsaturated fatty acid (PUFA) content of the different tissues indicated complex interactions between nutrient availability and metabolic adaptation.

Increased alpha-linolenic acid intake lowers C-reactive protein, but has no effect on markers of atherosclerosis

OBJECTIVE

To investigate the effects of increased alpha-linolenic acid (ALA)-intake on intima-media thickness (IMT), oxidized low-density lipoprotein (LDL) antibodies, soluble intercellular adhesion molecule-1 (sICAM-1), C-reactive protein (CRP), and interleukins 6 and 10.

DESIGN

Randomized double-blind placebo-controlled trial.

SUBJECTS

Moderately hypercholesterolaemic men and women (55 +/- 10 y) with two other cardiovascular risk factors (n = 103).

INTERVENTION

Participants were assigned to a margarine enriched with ALA (fatty acid composition 46% LA, 15% ALA) or linoleic acid (LA) (58% LA, 0.3% ALA) for 2 y.

RESULTS

Dietary ALA intake was 2.3 en% among ALA users, and 0.4 en% among LA users. The 2-y progression rate of the mean carotid IMT (ALA and LA: +0.05 mm) and femoral IMT (ALA:+0.05 mm; LA:+0.04 mm) was similar, when adjusted for confounding variables. After 1 and 2 y, ALA users had a lower CRP level than LA users (net differences -0.53 and -0.56 mg/l, respectively, P < 0.05). No significant effects were observed in oxidized LDL antibodies, and levels of sICAM-1, interleukins 6 and 10.

CONCLUSIONS

A six-fold increased ALA intake lowers CRP, when compared to a control diet high in LA. The present study found no effects on markers for atherosclerosis.

SPONSORSHIP

The Dutch 'Praeventiefonds'.

Differential effects of dietary fatty acids on the regulation of CYP2E1 and protein kinase C in human hepatoma HepG2 cells

We investigated the effects of different fatty acids (FAs) or with different degrees of unsaturation on cytochrome P450 2E1 (CYP2E1) induction and protein kinase C (PKC) activity in human hepatoma HepG2 cells. As the degree of unsaturation increased, the cell survival rate decreased for FAs with 18 carbons, but linolenic acid (LNA) or docosahexaenoic acid (DHA) groups were similar even through they have different degrees of unsaturation. Treatment with palmitic acid (PA), oleic acid (OA), linoleic acid (LA), LNA, and DHA resulted in respective cellular FA concentrations of C16:0 (43.1%), C18:1 (18.5%), C18:2 (7.4%), LNA (2.85%), and C22:6 (3.13%), which was highest for the FA that was used as the treatment, indicating that their incorporation within the cell is directly proportional to treatment. After 2 hours of cultivation, the lipid peroxide (LPO) in the DHA group increased 600% compared with control, and was much higher than in the groups treated with the other FAs, with LNA > LA > OA > PA. CYP2E1 induction increased with greater effect as the degree of unsaturation of OA, LA, and DHA increased. PA did not affect PKC activity, but DHA treatment increased PKC activity the most. The effects of LNA and LA were similar, but less than that of DHA, and that of OA was lower still, indicating that activity of PKC is proportional to the degree of unsaturation, and not the configuration of the FA. Increased plasma membrane concentrations of n-3 FA, such as DHA, might exert regulatory effects on PKC by increasing membrane fluidity, causing changes in CYP2E1, elevating levels of LPO, or producing oxidative stress.

Effects of Substrate, Passage Rate, and pH in Continuous Culture on Flows of Conjugated Linoleic Acid and Trans C18:1

A dual-flow continuous culture system consisting of 4 fermenters was used in a 4 x4 Latin square design. The objective of the research was to evaluate the effects of solid dilution rate (SDR), pH, and concentration of linoleic acid (LA) in the feed mixture on the production of conjugated linoleic acid (CLA) and trans-C18:1. The 4 treatments were 1) control = pH 6.5, 1% LA, 4%/h SDR; 2) high solid dilution rate (HSDR) = pH 6.5, 1% LA, 8%/h SDR; 3) high linoleic acid (HLA) = pH 6.5, 3% LA, 4%/h SDR; and 4) low pH (LPH) = pH 5.8, 1% LA, 4%/h SDR. Inoculum was collected 6 h after feeding from a cow fed 40% alfalfa hay and 60% grain. Liquid dilution rate was held at 0.12/h. All treatments except HLA contained 2% tallow. The LA was dissolved in buffer and continuously infused into the fermenters. The CLA flows were 16.5, 20.4, 23.2, and 25.2 mg/d for control, HSDR, HLA, and LPH, respectively. Compared with control, LPH increased flows of CLA, cis-C18:1, and C18:2, and decreased flow of C18:0. The neutral detergent fiber (NDF) and acid detergent fiber (ADF) digestibilities were not affected by pH. The HSDR tended to increase CLA flow compared to control, possibly because a shorter solid retention time led to incomplete biohydrogenation (BH). The NDF and ADF digestibilities and bacterial numbers were reduced by HSDR. With more LA available as a substrate for CLA, HLA resulted in a higher flow of CLA than control. The HLA resulted in the highest acid detergent fiber and fatty acid digestibilities, bacterial numbers, and BH. Increasing solids passage rate, reducing pH, and increasing dietary LA appears to increase in vitro CLA production.

Conjugated linoleic acid prevents the development of essential hypertension in spontaneously hypertensive rats

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of linoleic acid found in beef, lamb, and dairy products. CLA has attracted considerable attention over the past several decades because of its potentially beneficial biologic effects, including protective effects against several cancers, atherosclerosis, and obesity. In previous studies, we provided evidence that dietary CLA could prevent the development of obesity-related hypertension in obese animals. Here, we show that CLA suppresses the development of non-obese essential hypertension in spontaneously hypertensive rats (SHRs). After 4 weeks of feeding with CLA, the increase of systolic blood pressure was significantly suppressed compared with rats fed linoleic acid. Abdominal adipose tissue weight was also significantly lowered in CLA-fed SHRs. Content of arachidonic acid, the substrate of eicosanoid production, was not changed, but accumulation of oleic acid, the lipogenesis end-product, was markedly decreased in the membrane phospholipids of CLA-fed SHRs. In addition, we found increased level of plasma adiponectin, suggested as a regulatory factor of hypertension, through the enhancement of mRNA expression in CLA-fed SHRs. We speculate that the antihypertensive effect of dietary CLA may be due to the increase of plasma adiponectin level and associated with the alleviation of membrane abnormality in SHRs.

Effect of diet and dietary fatty acids on the transformation and incorporation of C18 fatty acids in double-muscled Belgian Blue young bulls

Three groups of double-muscled Belgian Blue young bulls were fed during different stages of production diets differing in the proportions of linolenic and linoleic acid by including linseed in the concentrate or giving grass silage as main linolenic acid suppliers. Samples of rumen and abomasal contents and of the longissimus thoracis, subcutaneous fat, and liver were taken to analyze the fatty acid pattern with emphasis on the individual trans (t) C18:1 fatty acids and cis-9,trans-11 conjugated linoleic acid (c9t11CLA). Trans C18:1 isomers represented up to 20 g/100 g of total fatty acids in rumen and abomasal contents, whereas the accumulation of c9t11CLA was limited. Total trans C18:1 content in subcutaneous fat and intramuscular fat of the longissimus thoracis comprised 8.4 and 5.2 g/100 g of total fatty acids, respectively, with t11C18:1 being the most abundant one. Compared to rumen contents, subcutaneous and intramuscular fat were enriched in c9t11CLA and contained fewer tC18:1 isomers, resulting in a higher c9t11CLA/t11C18:1 ratio (0.04, 0.22, and 0.22, respectively). This result suggests that the endogenous synthesis of c9t11CLA in adipose tissue by the Delta(9)-desaturase was more important than its ruminal production.

The role of insulin, glucagon, dexamethasone, and leptin in the regulation of ketogenesis and glycogen storage in primary cultures of porcine hepatocytes prepared from 60 kg pigs

A study was conducted to elucidate hormonal control of ketogenesis and glycogen deposition in primary cultures of porcine hepatocytes. Hepatocytes were isolated from pigs (54-68 kg) by collagenase perfusion and seeded into collagen-coated T-25 flasks. Monolayers were established in medium containing fetal bovine serum for 1 day and switched to a serum-free medium for the remainder of the culture period. Hepatocytes were maintained in DMEM/M199 containing 1% DMSO, dexamethasone (10(-6) or 10(-7) M), linoleic acid (3.4 x 10(-5) M), and carnitine (10(-3) M) for 3 days. On the first day of serum-free culture, insulin was added at 1 or 100 ng/ml and glucagon was added at 0, 1, or 100 ng/ml. Recombinant human leptin (200 ng/ml) was added during the final 24 h; medium and all cells were harvested on the third day. Concentrations of acetoacetate and beta-hydroxybutyrate (ketone bodies) in media and glycogen deposition in the cellular compartment were determined. Ketogenesis was highly stimulated by glucagon (1 and 100 ng/ml) and inhibited by insulin. In contrast, glycogen deposition was stimulated by insulin and attenuated by glucagon; high insulin was also associated with a reduction in the ketone body ratio (acetoacetate:beta-hydroxybutyrate). High levels of dexamethasone stimulated ketogenesis, but inhibited glycogen deposition at low insulin. Culture of cells with leptin for 24 h, over the range of insulin, glucagon, and dexamethasone concentrations had no effect on either glycogen deposition or ketogenesis. These data suggest that while adult porcine hepatocytes are indeed sensitive to hormonal manipulation, leptin has no direct influence on hepatic energy metabolism in swine.

In vivo oxidation of carboxyl-labelled cyclic fatty acids formed from linoleic and linolenic acids in the rat

Cyclic fatty acid monomers (CFAM), which occur from the intramolecular cyclisation of linoleic and linolenic acids, are subsequently present in some edible oils and are suspected to induce metabolic disorders. One may suggest that the presence of a ring would alter the ability of the organism to oxidise these molecules. In order to test this hypothesis, we assessed the oxidative metabolism of CFAM in rats. For this purpose, rats were force-fed from 1.5 to 2.6 MBq of [1-(14)C]-linoleic acid, [1-(14)C]-linolenic acid, [1-(14)C]-CFAM-18:2 or [1-(14)C]-CFAM-18:3, and 14CO2 production was monitored for 24 h. The animals were then sacrificed and the radioactivity was determined in different tissues. No significant differences in 14CO2 production were found 24 h after the administration of CFAM and their respective precursors. Our data clearly demonstrate that, at least for the first beta-oxidation cycle, CFAM are oxidised in a similar way as both essential fatty acids.

Diet and melanoma in a case-control study

BACKGROUND

Malignant melanoma has been one of the most rapidly increasing cancers within the United States with few modifiable risk factors. This study investigates risk related to dietary factors, which are potentially modifiable.

METHODS

Newly diagnosed patients with melanoma (n = 502) were recruited from pigment lesion clinics and controls (n = 565) were recruited from outpatient clinics. To investigate the relationship between melanoma and dietary factors in this case-control study, study subjects were requested to complete a food frequency questionnaire, which assessed diet over the previous year. Using logistic regression, odds ratios (ORs) for melanoma were computed for nutrient and alcohol intake.

RESULTS

Persons in high versus low quintiles of energy-adjusted vitamin D, alpha-carotene, beta-carotene, cryptoxanthin, lutein, and lycopene had significantly reduced risk for melanoma (ORs < or = 0.67), which remained after adjustment for presence of dysplastic nevi, education, and skin response to repeated sun exposure. Addition of micronutrients from supplements did not add an additional reduction in risk. High alcohol consumption was associated with an increased risk for melanoma, which remained after adjustment for confounders [OR (95% confidence interval) in highest versus lowest quintiles, 1.65 (1.09-2.49)].

CONCLUSIONS

Diets consisting of foods rich in vitamin D and carotenoids and low in alcohol may be associated with a reduction in risk for melanoma. These analyses should be repeated in large, prospective studies.

No difference in platelet activation or inflammation markers after diets rich or poor in vegetables, berries and apple in healthy subjects

BACKGROUND

High intake of vegetables and fruits is associated with decreased risk of coronary heart disease. Part of these cardioprotective effects may be mediated via the antithrombotic effects of compounds found in vegetables and fruits, such as flavonoids.

AIM OF THE STUDY

To study the effects of high and low intake of vegetables, berries and apple on platelet function and inflammatory markers.

METHODS

The study was a randomised, controlled parallel human dietary intervention with healthy female and male volunteers (n = 77, 19-52 y). Nineteen healthy volunteers served as controls. The volunteers consumed one of four strictly controlled isocaloric 6-week diets containing either 810 or 196 g/10 MJ of vegetables, berries and apple and rich either in linoleic acid (11% of energy, en%) or oleic acid (12 en%). Blood and three 24-hour urine samples were collected at the beginning and at the end of the study period for analyses of various markers of platelet function and inflammation.

RESULTS

No differences between the treatment groups were seen in platelet count or volume, markers of platelet activation ( ex vivo aggregation to ADP and thrombin receptor activating peptide, protein kinase C activity, urinary 2,3-dinor-thromboxane B2 excretion, plasma P-selectin), plasma intercellular adhesion molecule-1, sensitive C-reactive protein, or antiphospholipid antibodies.

CONCLUSIONS

The results indicate that in healthy volunteers 6-week diets differing markedly in the amounts of vegetables, berries and apple do not differ in their effects on platelets or inflammation.

Regulation of selenoprotein GPx4 expression and activity in human endothelial cells by fatty acids, cytokines and antioxidants

Phospholipid hydroperoxide glutathione peroxidase (GPx4) is the only antioxidant enzyme known to directly reduce phospholipid hydroperoxides within membranes and lipoproteins, acting in conjunction with alpha-tocopherol to inhibit lipid peroxidation. Peroxidation of lipids has been implicated in a number of pathophysiological processes, including inflammation and atherogenesis. We investigated the relative positive and negative effects of specific polyunsaturated fatty acids (PUFAs) and inflammatory cytokines on the activity and gene expression of the selenium-dependant redox enzyme GPx4. In human umbilical vein endothelial cells (HUVEC), GPx4 mRNA levels and activity were increased optimally by 114 nM selenium (as sodium selenite). Docosahexaenoic acid (DHA) and conjugated linoleic acid (CLA) further increased mRNA levels whereas arachidonic acid (ARA) had no effect; enzyme activity was decreased by DHA, was unaffected by CLA or was increased by ARA. GPx4 protein levels increased with selenium, ARA and DHA addition but not with CLA. Interleukin-1beta (IL-1beta) increased GPx4 mRNA, protein and activity whereas TNFalpha at 1 ng/ml increased activity while at 3 ng/ml it reduced activity and mRNA. Conversely, alpha-tocopherol reduced mRNA levels without affecting activity. These results indicate that lipids, cytokines and antioxidants modulate GPx4 in a complex manner that in the presence of adequate selenium, may favour protection against potentially proatherogenic processes.

Manipulation of the n-3 polyunsaturated fatty acid content of muscle and adipose tissue in lambs1

Fifty Suffolk-crossbred wether lambs, with an initial live weight of 29 +/- 2.1 kg, were allocated to one of five concentrate-based diets formulated to have a similar fatty acid content (60 g/kg DM), but containing either linseed oil (high in 18:3n-3); fish oil (high in 20:5n-3 and 22:6n-3); protected linseed and soybean (PLS; high in 18:2n-6 and 18:3n-3); fish oil and marine algae (fish/algae; high in 20:5n-3 and 22:6n-3); or PLS and algae (PLS/algae; high in 18:3n-3 and 22:6n-3). Lambs were slaughtered when they reached 40 kg. Growth performance and intake were similar (P > 0.35) among treatments. By contrast, gain:feed was higher (P < 0.05) in lambs fed the fish oil compared with the linseed oil or PLS/algae diets. Total fatty acid concentration (mg/100 g) in the neutral lipid of the longissimus muscle was not affected by treatment (P > 0.87) but was least (P < 0.05) in the phospholipid fraction in lambs fed the linseed oil diet. Lambs fed either diet containing marine algae contained the highest (P < 0.05) percentage of 22:6n-3 in the phospholipid (mean of 5.2%), 2.8-fold higher than in sheep fed the fish oil diet. In lambs fed the fish/algae diet, the percentage of 20:5n-3 was highest (P < 0.05), contributing some 8.7, 0.8, and 0.5% of the total fatty acids in the muscle phospholipid, neutral lipids, and adipose tissue, respectively. The percentage of 18:3n-3 in the phospholipid fraction of the LM was highest (P < 0.05) in lambs fed the linseed oil diet (6.9%), a value double that of sheep fed the PLS diet. By contrast, lambs fed the PLS diet had twice the percentage of 18:3n-3 in the muscle neutral lipids (3.8%) than those offered the linseed oil diet, and 5.5-fold greater than lambs fed the fish/algae treatment (P < 0.05), an effect that was similar in the adipose tissue. The percentage of 18:2n-6 was highest (P < 0.05) in lambs fed the PLS diet, where it contributed 33.7, 10.1, and 11.2% in the muscle phospholipid, neutral lipids, and adipose tissue, respectively. The highest (P < 0.05) muscle PUFA-to-saturated fatty acid (P:S) ratio was obtained in lambs fed the PLS diet (0.57), followed by the PLS/algae diet (0.46), and those fed the fish oil or linseed oil diets had the lowest ratios (0.19 and 0.26, respectively). The favorable P:S ratio of lambs fed the PLS/algae diet, in conjunction with the increased levels of 20:5n-3 and 22:6n-3, enhanced the nutritional qualities of lamb to more closely resemble what is recommended for the human diet.

No relations between breast cancer risk and fatty acids of erythrocyte membranes in postmenopausal women of the Malmö Diet Cancer cohort (Sweden)

OBJECTIVE

To examine the fatty acid composition of erythrocyte membranes, in relation to obesity indexes and breast cancer risk.

DESIGN

A nested case-control study.

SETTING

The Malmö Diet Cancer cohort, Sweden.

SUBJECTS

Among women 50 y or older at baseline (n=12 803), incident breast cancer cases (n=237) were matched to controls (n=673) on age and screening date.

METHODS

A diet history method, a structured questionnaire, anthropometrics and blood samples provided data. Analysis included partial correlation coefficients between dietary fatty acids (DFA) and fatty acids of erythrocyte membranes (EFA), and Spearman's rank order correlations between EFA and four obesity indexes. Conditional logistic regression examined breast cancer risks related to EFA.

RESULTS

DFA and EFA from fish and milk, and DFA and EFA linoleic acid, show significant positive associations. Relations are negative between indexes of obesity and "milk" EFA, but positive between indexes of obesity and indexes of delta9- and delta6-desaturase enzyme activity. No significant relations were observed between EFA and breast cancer risk.

CONCLUSIONS

Similar to other studies, dietary fish and milk fatty acids, and linoleic acid, are related to the corresponding EFA. Breast cancer risk was not significantly related to EFA in this study. However, the findings suggest positive relations between body mass index, body fat per cent and indexes of desaturase activity, and negative relations between central obesity and milk EFA.

SPONSORSHIP

The Swedish Cancer Society, the Swedish Medical Research Council, the European Commission, the Swedish Dairy Association and the City of Malmö.

Fertility following fixed-time AI in CIDR-treated beef heifers given GnRH or estradiol cypionate and fed diets supplemented with flax seed or sunflower seed

The objectives were to determine pregnancy rates following fixed-time AI (FTAI) in heifers: (1). given GnRH or estradiol cypionate (ECP) to synchronize follicular wave emergence and ovulation in a CIDR-based protocol; and (2). fed diets supplemented with flax or sunflower seeds. At two locations, Angus and crossbred Angus heifers (n=983) were examined ultrasonically to confirm reproductive maturity and randomly allocated to six synchronization groups in a 2 x 3 factorial design. On Day 0 (start of synchronization treatments), heifers received a CIDR and either 100 microg GnRH i.m. (n=492) or 1mg ECP plus 50 mg progesterone i.m. (n=491); in these groups, CIDR removal and PGF treatment were done concurrently on Days 7 and 8.5, respectively. Heifers were re-randomized to receive 0.5 mg ECP i.m. at CIDR removal or 24 h later (with FTAI 58-60 h after CIDR removal in both groups), or 100 microg GnRH i.m. concurrent with FTAI (52-54 h after CIDR removal). The heifers were fed a barley silage-based diet for 50 days (from Day -25 to 25) supplemented with 1kg/heifer per day of flax seed (n=321), sunflower seed (n=324), or no oilseed (n=338). Pregnancy rate to FTAI (overall, 56.2%) was not affected by treatment at CIDR insertion (P = 0.96) but was higher (P < 0.05) in heifers given ECP 24h after CIDR removal (216/330, 65.4%) than in those given either ECP at CIDR removal (168/322, 52.1%) or GnRH at AI (169/331, 51.1%). Overall, there was no effect of diet on pregnancy rates (P = 0.46). In summary, pregnancy rate to FTAI was not significantly affected by treatment at CIDR insertion to synchronize follicular wave emergence, but 0.5mg ECP 24h after CIDR removal (to synchronize ovulation) resulted in the highest pregnancy rate.

Short Communication: Docosahexaenoic Acid Promotes Vaccenic Acid Accumulation in Mixed Ruminal Cultures When Incubated with Linoleic Acid

Previous studies found that feeding dairy cows a blend of fish and soybean oils enhanced milk vaccenic acid (VA) and conjugated linoleic acid (CLA) concentrations more than when the oils were fed separately. In these studies, the authors concluded that a component in fish oil was stimulating ruminal VA production from other sources of unsaturated fatty acids; however, that component was not identified. The objective of this study was to determine whether docosahexaenoic acid (DHA), an omega-3 fatty acid (FA) in fish oil, is the active component that promotes trans-C18:1 FA, VA in particular, accumulation using cultures of mixed ruminal microorganisms. Treatments consisted of control, control plus 5 mg of DHA (DH), control plus 30 mg of soybean oil (SBO), and control plus 5 mg of DHA and 30 mg of SBO (DHSBO). Treatments were incubated in triplicate in 125-mL flasks, and 5 mL of culture contents was taken at 0 and 24 h for fatty acid analysis by gas-liquid chromatography. After 24 h of incubation, the level of trans-C18:1 FA (14.1 and 11.7 mg/culture) and VA (13.0 and 10.2 mg/culture) increased more with added DHA than with added SBO, respectively. Combining DHA and SBO yielded higher quantities of trans-C18:1 FA (21.3 mg/culture) and VA (19.8 mg/culture) in the cultures than either fat source alone. These data suggest that DHA is the component in fish oil that promotes VA accumulation when incubated with linoleic acid.

Truncal and hepatic vagotomy reduce suppression of feeding by jejunal lipid infusions

Two experiments investigated mechanisms underlying the decrease in food intake produced by lipid infusions into the jejunum. In Experiment 1, male Sprague-Dawley rats with truncal abdominal vagotomy (TVx), selective hepatic-branch vagotomy (HVx), or sham vagotomy received repeated 7 h infusions of linoleic acid (LA), corn oil (CO), or saline through indwelling jejunal catheters. Cumulative food intake was measured at 1, 3, 6, and 23 h. LA and, to a lesser extent, CO suppressed food intake in excess of the caloric value of the load. This effect was eliminated by TVx, which significantly attenuated the suppression of intake produced by both lipids at 3 and 6 h and also at 23 h when LA was infused. HVx attenuated suppression at 23 h on tests with LA and at 3 and 6 h on CO tests. Experiment 2 showed that jejunal infusion of LA had no effect on multi-unit activity of afferent fibers in the left splanchnic nerve in anesthetized rats. Thus, these results provide further evidence that satiating effects of intestinal lipid infusions are mediated by the vagal fibers, some of which lie within the hepatic branch. However, because significant suppression of food intake remained after TVx, and because of the negative results of Experiment 2, these lipid infusions engage as yet unidentified mechanisms independent of the vagus.

Influence of topical administration of n-3 and n-6 essential and n-9 nonessential fatty acids on the healing of cutaneous wounds

Injury triggers a series of physiological events at the wound site. These include an inflammatory response that is established shortly after the injury, which is then followed by an intense formation of tissue over a period of days. Poly- and monounsaturated fatty acids exert major functions on the inflammatory responses, either in the form of phospholipids anchored in the cell membrane or as soluble lipoic mediators. We present evidence that linolenic (n-3), linoleic (n-6), and oleic (n-9) fatty acids can modulate the closure of surgically induced skin wounds. We found that n-9 fatty acids induced faster wound closure when compared to n-3, n-6, and control. In addition, n-9 fatty acids strongly inhibited the production of nitric oxide at the wound site. A mild improvement on wound closure was observed in the n-6 fatty acid-treated animals concurrent with a peak in nitric oxide production at 48 hours postsurgery. N-3 fatty acid treatment significantly delayed wound closure. Furthermore, we showed that n-3 fatty acid induced a peak in nitric oxide at 3 hours postsurgery and an intense deposition of extracellular matrix after 5 days of treatment. Thus, our results suggest a relevant role and potential therapeutic implication for fatty acids on skin wound healing.

Influence of temperature and high dietary linoleic acid content on esterification, elongation, and desaturation of PUFA in Atlantic salmon hepatocytes

The esterification, desaturation, and elongation of [1-14C]18:3n-3, [1-14C]18:2n-6, and [1-14C]20:5n-3 at 5 and at 12 degrees C were studied using cultivated hepatocytes from Atlantic salmon. The salmon were fed diets, in which 0, 50, or 100% of the supplementary fish oil had been replaced by soybean oil, for 950 day-degrees at 5 and 12 degrees C. The endogenous percentage of 18:2n-6 in hepatocyte lipids was 2% in cells from fish fed a diet with 100% of the supplemental lipid from fish oil, and it was slightly less than 25% in cells from fish fed the diet with 100% of the supplemental lipid from soybean oil. Furthermore, the percentages of 20:3n-6 and 20:4n-6 were significantly higher in hepatocytes from fish fed on soybean oil than they were in those of fish fed on fish oil. The percentages of 20:5n-3 and 22:6n-3, on the other hand, were lower. The endogenous levels of n-6 FA were not significantly correlated with the total amounts of radiolabeled FA esterified in hepatocyte lipids. The main radiolabeled products formed from 18:2n-6 were 20:2n-6 and 20:3n-6. The level of the important eicosanoid precursor 20:4n-6 was twice as high in hepatocyte phospholipids from fish fed the 100% soybean oil diet as it was in hepatocytes from fish fed the diet with 100% of supplemental lipid from fish oil. The main products formed from 18:3n-3 were 20:4n-3, 20:5n-3, and 22:6n-3. High levels of dietary 18:2n-6 do allow, or even seem to increase, the production of 22:6n-3 from 18:3n-3 in hepatocytes. The main products formed from 20:5n-3 were 22:5n-3 and 22:6n-3. The production of 22:6n-3 from 20:5n-3 was higher at 5 degrees C than at 12 degrees C. The percentage of 24:5n-3 was higher at 5 degrees C than it was at 12 degrees C, as was the ratio of 24:5 to 22:5. These results suggest that the elongation rate of 22:5n-3 to 24:5n-3 is higher at the lower temperature.

Jejunal administration of linoleic acid increases activity of neurons in the paraventricular nucleus of the hypothalamus

The present experiment examined whether neurons located in the paraventricular nucleus of the hypothalamus (PVN) respond to intestinal infusions of long-chain fatty acids. Single-unit recordings were made of neurons located in and adjacent to the PVN during jejunal administration of linoleic acid. Jejunal administration of linoleic acid increased single-unit activity of neurons located in the PVN but did not affect activity of neurons located in adjacent tissue outside the PVN. The largest increases in neuronal activity were observed in the anterior PVN (0.9-1.3 mm posterior to bregma) compared with the posterior PVN (1.8-2.1 mm posterior to bregma). Jejunal administration of saline failed to affect activity of neurons located either inside or outside the PVN. When the same neurons were subsequently tested for their response to intravenous administration of 2 microg/kg of CCK-8, excitatory responses were more frequently observed than inhibitory responses, but both types of responses were observed regardless of whether neurons were located inside or outside the PVN. In addition, there was no strong correlation between the magnitude of the neuronal response evoked by jejunal administration of linoleic acid compared with intravenous CCK-8. These data suggest that neurons located in the anterior PVN may play a role in the mediation of suppression of food intake produced by intestinal administration of lipids.

Dietary linoleic acid-induced hypercholesterolemia and accumulation of very light HDL in steers

This experiment was designed to study the effects in fattening steers of n-6 PUFA supplementation on the plasma distribution and chemical composition of major lipoproteins (TG-rich lipoproteins: d < 1.006 g/mL; intermediate density lipoproteins + LDL: 1.019 < d < 1.060 g/mL; light HDL: 1.060 < d < 1.091 g/mL; and heavy HDL: 1.091 < d < 1.180 g/mL). For a period of 70 d, animals [454 +/- 20 d; 528 +/- 36 kg (mean +/- SD)] were given a control diet (diet C, n = 6) consisting of hay and concentrate mixture (54 and 46% of diet dry matter, respectively) or the same diet supplemented with sunflower oil (4% of dry matter), given either as crushed seeds (diet S, n = 6) or as free oil continuously infused into the duodenum through a chronic canula to avoid ruminal PUFA hydrogenation (diet O, n = 6). Plasma lipids increased in steers given diet S (x1.4, P < 0.05) and diet O (x2.3, P < 0.05), leading to hyperphospholipemia and hypercholesterolemia. With diet S, hypercholesterolemia was associated with higher levels of light (x1.4, P < 0.05) and heavy HDL (x1.3, NS). With diet O, it was linked to higher levels of light HDL (x1.8, P < 0.005) and to very light HDL accumulation within density limits of 1.019 to 1.060 g/mL, as demonstrated by the apolipoprotein A-I profile. Diet O favored incorporation of 18:2n-6 into polar (x2.2, P < 0.05) and neutral lipids (x1.5 to x8, P < 0.05) at the expense of SFA, MUFA, and n-3 PUFA. Thus, protection of dietary PUFA against ruminal hydrogenation allowed them to accumulate in plasma lipoproteins, but the effects of hypercholesterolemia on animal health linked to very light HDL accumulation remain to be elucidated.

Influence of a maternal cholesterol-enriched diet on [1-14C]-linoleic acid and L-[4, 5-3H]-leucine entry in plasma of rabbit offspring

Fetal development requires an important entry of essential free fatty acids (EFFA) and essential amino acids (EAA) into the fetal circulation. We have reported that a 0.2% enriched-cholesterol diet (ECD) during rabbit gestation significantly reduces fetus weight compared to control diet. It is known that dietary linoleic acid deficiency, an EFFA, during the fetal development induces an important impair to the somatic development. Moreover, intrauterine growth retardation induced a reduction of the flux of leucine, an EAA, from maternal to fetal circulation. Therefore, we hypothesized that the administration of an ECD induces modifications of placental lipid composition concomitant alterations of the transfer of linoleic acid and leucine in fetal circulation. Quantification of placental lipids revealed that in the ECD group a reduction of total-cholesterol (TC) and free-cholesterol (FC) is observed, however an increased in FFA and phospholipids is noticed when compared to the control group. In placenta from the ECD group, the FC/ TC ratio is significantly reduced compared to the control group. In the ECD group, the liver shows an increase of TC, FC and FFA compared to the control group. However, the quantity of triacylglycerol present in the liver from the ECD is significantly reduced compared to the control group. To evaluate the placental transfer of some essential nutrients, intravenous injection of [1-14C]-linoleic acid or L-[4, 5-3H]-leucine to term rabbit (control and ECD group) were done. Two hours later, rabbits were euthanized and we collected placenta, livers and blood from dams and offspring. The concentrations of both radiolabeled molecules (linoleic acid and its esterified form or leucine) were higher in the plasma of ECD offspring than those found in offspring from control diet. Despite such alteration of placental lipid composition, linoleic acid and leucine transfer by the placenta was not compromised but rather increased.

Dietary protein modulates the effect of CLA on lipid metabolism in rats

The effect of the interaction of CLA and type of dietary protein on lipid metabolism was studied in male rats by feeding diets containing casein (CAS) or soy protein (SOY) as dietary protein and either linoleic acid (LA, a control FA) or graded levels of CLA at 0, 0.1, 0.5, and 1.0% for 28 d. CLA reduced the weight of perirenal adipose tissue in a dose-dependent manner, but the magnitude of the reduction was greater when rats were fed SOY. Feeding SOY resulted in a significant reduction of the concentrations of serum total and HDL cholesterol, TG, glucose, and insulin irrespective of dietary CLA. The concentration of serum leptin tended to be lower on the SOY diet free of CLA than in the corresponding CAS diet, but it fell with an increasing dietary level of CLA in the CAS groups. In contrast, serum leptin tended to increase when CLA was added to SOY diets. The concentration of serum adiponectin was higher in the CAS than in the SOY groups, and it tended to increase in response to dietary CLA levels in the CAS-fed rats, whereas CLA showed no effect in SOY-fed rats. The activity of liver mitochondrial carnitine palmitoyltransferase was higher in the SOY than in the CAS groups, but it tended to increase with an increasing dietary level of CLA in both protein groups. Although the body fat-reducing activity of CLA was more effective when the protein source was SOY, rats fed CAS appeared to be more susceptible to CLA than in those fed SOY with respect to cytokines examined. These results suggest that the type of dietary protein may modify the antiobesity activity of CLA.